Cleaning solution and method



United States Patent Ofii e 2,700,654 Patented Jan. 25, 1955 2,700,654 I CLEANING SOLUTION AND METHOD No Drawing. Application April 1, 1947, Serial No. 738,731

2 Claims. (Cl. 252-118) This invention has to do with cleaning solutions for metallic surfaces, particularly those surfaces which by their construction are inaccessible by the usual cleaning methods, such as cooling coils, heat exchanger coils, unit heaters, etc., and while not intended to be so limited in its use, is peculiarly adapted to the cleaning of oil coolers of airplane engines and the like which present a rather complex cleaning problem. No solution heretofore has been found which is capable of performing this complex cleaning operation in a single treatment.

As is well known, in oil coolers, which are placed between the engine and oil reservoir, the oil flows in relatively thin films through narrow interstices provided between small copper cooling tubes, the oil being guided and deflected by baflles. The heat transfer surfaces become coated with carbon, oxidized oil, corrosion products and the like, which materially reduce the heat exchange, and insuflicient cooling of the coil is apt to result in power reductions which may be disastrous, particularly in a combat plane. For instance, it is estimated that from 2% to 5% of the brake horsepower of the engine is transmitted in the form of heat to the lubricating oil and the major portion of this heat must be removed in the oil cooler. Particles of bearing metal are also found in the cooler and if these continue to circulate in the lubricating oil they may be expected to abrade the bearings and cause engine failure. These solids sometimes adhere to the bafiies or tubes in the cooler and the bonding element must be dissolved. Abrasive grit and dust are also present in the deposit.

The cleaning problem thus presented is therefore one of removing carbon, oxidized oil, dislodging metal particles, and removing dust, grit and corrosion products. Removal of the insoluble solids requires a solvent for the bonding material causing the solids to adhere to the metal surfaces. The solvents most generally used for this purpose are carbon tetrachloride, trichlorethylene, ethylene dichloride, cresylic acid, alcohols andthe like, and, while reasonably effective, they do not remove the products of copper corrosion because the latter are insoluble in such solvents and neither do such solvents exert any appreciable softening or loosening action thereon. Consequently, heretofore such corrosion products have either remained on the heat exchange surfaces or an additional operation has been performed to remove them, such as disassembling the tubes and mechanically polishing them with steel wool. In some cases the tubes have been subjected to a subsequent circulation of a sulphuric or muriatic acid solution or a solution of sodium or potassium cyanide, but such chemicals are poisonous, corrosive, are difiicult to handle with ordinarily available equipment, and are less effective than desirable. Furthermore, they present the danger of reducing the metal thickness of the tubes to a dangerous point which may result in mechanical failure.

Those working in this art have long sought a cleaning solution and method which is free of use hazards and is capable of removing all the soiling elements, including the corrosion products, in a single cleaning operation, thus eliminating the hazardous subsequent separate sulphuric acid or cyanide treatment.

Accordingly it is an object of the present invention to provide a composition and method particularly applicable for cleaning such complex carbonaceous deposits from metal surfaces as are not directly accessible to mechanical scouring. In particular there is provided a solution in which aircraft engine cooler tubes and like objects may be soaked for a comparatively short time and the property of such then rinsed clean of soot, oil, dirt and metallic corrosion products simply by flushing with water or steam. Additional objects will be apparent as the description proceeds.

My invention is based upon the utilization of a liquid mixture or solution of an oleaginous solvent for the oil decomposition products, a soap which acts as a detergent and emulsifying agent, and a small quantity of Water, plus an amount of a water soluble, free primary amine in excess of that used up in neutralizing any acid present in the deposit being removed. Optionally there is also present a coupling agent or mutual solvent for oil and water.

Although numerous soaps, including amine soaps, as well as free amines have been used at times in somewhat analogous cleaning operations, I have found that a highly unexpected result is obtained by the present combination of a soap, and particularly an amine soap, with free amine, when the latter is a primary amine, (RNHz), since the cleaning effect produced by such combination is greatly in excess of any additive or expected result anticipated from using the two individually. The salient property of the free amine is to attack the products of metallic corrosion which are neither oil nor water soluble.

Without wishing to be bound by any theory of reaction, it appears likely that the unique result is correlated with primaryamines to form complexes or coordination compounds with metals such as copper, cadmium, nickel, cobalt, zinc and possibly silver, such complexes then being rendered Water soluble due to the presence of the aqueous amine component. However,

I an additional contributing factor to the exceptional results obtained is found in the joint actions of the free or uncombined amine and the soap. The soap employed may be either a monovalent metallic soap or an amine soap and it is possible that use of an amine soap contributes to the penetrating ability of the free amine, allowing it to better reach the metallic corrosion products. However, when the soap used is an amine soap, the combined amine portion of it need not correspond to the necessary requirements for the free, water soluble amine, but need only have a minimum water solubility of about 1%.

The free amines employed in the present procedure are chiefly primary amines having a maximum of about four to six carbon atoms so as to render them water soluble. If the higher molecular weight members in this range are employed, preferably it is in admixture with larger amounts of lower molecular weight ones so as to increase the solubility thereof. The amines may be straight chain, branched, or even cyclic, saturated or unsaturated, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, or tertiary butyl, the several pentyls including cyclopentyl, the corresponding alkynol amines, etc., and may be mono or poly amines, of which the diamines are especially useful.

The poly amines may have a slightly greater number of carbon atoms than noted above and still be effective due to the increased number of primary NH2 groups in the molecule, such polyamines including ethylene diamine, propylene diamine, mono methyl ethylene diamine, mono ethyl diethylene diamine, 1-l di methyl ethylene diamine, amino ethylethanolamine, di ethylene triamine, tri ethylene tetramine, and tetraethylene pentamine. In general, alkyl-, alkenyl-, alkynyl-, alkadienyl, and/or aryl-primary amines, whose solubility in water is greater than about 1% are applicable. A preferred range of the free amine in the composition is about 1% to 30% of the total weight, so as to leave an excess after neutralization of any free acidity present in the deposit being treated. If amine soap is also used, the total of free and combined amine should be a minimum weight of about 3%.

The cationic constituent of the soap may be a metallic radical such as sodium, potassium, ammonium or may, as stated, he an amine, such as one or more primary, secondary, tertiary or even quaternary amines, saturated or unsaturated. Cyclic amines include those derived from morpholine, pyridine, furane, cyclopentane, benzene and their various substituted products and derivatives. Generally the anionic constituent of the soap is a fatty acid of about 12 to 18 carbon atoms. Such anionic examples include caproic, capric, sebacic, cerotic, crucic, melissic, stearic, oleic, ricinoleic, linoleic, linolenic, lauric, myristic, palmitic, as well as mixed fatty acids derived from animal or vegetable sources such as lard, coconut ol, sesame oil, palm oil, olive oil, peanut oil, soya bean oil, castor oil, seal, whale and fish oils and the like. The corresponding sulfonated or sulfated products may likewise be employed. Preferred ranges of the soap are about 5% to 50%, by weight.

Suitable oleaginous or grease solvents which may be used to dissolve or suspend the oil decomposition products are well known in the art and include neutral coal tar oil, creosote oils, solvent naphthas, wood tar oils, coal tar hydrocarbon, petroleum hydrocarbons, hydrogenated petroleum solvents, hydroaromatic solvents and chlorinated aliphatic and aromatic solvents, which need not be free from hydroxy, ketone, carbonyl and other groups. Suitable concentration for the oleaginous solvent is on the order of about to 90%, by weight.

Suitable coupling agents or neutral solvents for oil and water include the well-known glycol ethers such as ethylene glycol mono or di alkyl ethers and di ethylene glycol mono alkyl ethers where alkyl is generally methyl, ethyl, butyl, etc. Pine oil, cresol, and/or cresylic acids may likewise be used, suitable quantities of such coupling agents being on the order of about 5% to The amount of water in the composition may be relatively small, being on the order of about 3% to 20%, but where the composition is applied as an emulsion, the Water becomes the major ingredient and may constitute upwards of 90% of the circulating fluid in extreme cases. The water serves to dissolve the soluble metal-amino complexes which are formed by reaction of the free primary amines with the metal oxides and other corrosion products. Although such metal-amino complexes have a limited solubility in anhydrous fluid containing excess free amine, I find that the detergent power of the composition abruptly increases beyond any expected improvement when the water content reaches 3% or more.

Compositions ranging from anhydrous to 4% water content are applied to advantage in cleaning devices operating from a surge tank, where the units being cleaned are then given a subsequent steam or water rinse which removes the metal-amino complexes, and the composition is stored for repetitive use hardly contaminated with heavy metal compounds. The reduction of water in the composition favors faster penetration and dissolution of greasy, resinous or organic binders in the deposit while it markedly reduces the solubility of the inorganic binders, but the steam or water rinse makes up for the latter deficiency. My composition may be circulated undiluted through tubing or the like being cleaned, and may then be rinsed with organic solvents, lubricating oil, water or steam, or it may be extended with water first and applied as an emulsion.

Application of my mixture is, of course, not limited to cleaning of metallic surfaces which cannot be scoured by hand, but in the event that exposed metal is available for mechanical cleaning a further advantageous result may be obtained by including in my composition an abrasive polishing agent such as bentonite, diatomaceous earth, chalk, tripoli, and the like, an amount on the order of about 50% to 90% being quite adequate, although much smaller quantities are also effective.

In a presently preferred example of my invention I use, by weight:

Per cent Ethylene diamine 12 Water 4 Neutral coal tar oil 68 Oleic acid 6 Pine oil 10 The neutral coal tar oil which I use in the above example 1s a fraction distilling between 190 and 315, from which tar acids such as phenols, xylenols, etc., have been removed, this having been found particularly advantageous for removing aircraft engine deposits.

A correspondingly effective formula is, by weight:

Per cent Aqueous ethylene diamine 13.83 Neutral coal tar oil 60.37 Oleic acid 11.20 Ethylene glycol monobutyl ether 6.82 Pine oil 7.78

The metallic parts may be soaked in the solution any desired length of time before being removed and flushed with water. However, the effectiveness of the solution permits practically complete removal of most engine deposits in a comparatively short time. Thus copper, aircraft oil temperature regulator tubes containing a heavy carbonaceous deposit accumulated in actual aircraft operation were immersed in the above solution for 25 minutes at F. Upon their being withdrawn and washed with water, the copper presents a gleaming, bright ap-. pearance. Similar tests with comparable cleaners which lacked free primary amines or wherein my excess amine was replaced by an oil-soluble or higher substituted (i. e. secondary or tertiary) amine removed but a small fraction of the total Weight of deposit and the clean areas presented a dull and unsatisfactory appearance. The composition can similarly be used at ordinary room temperature, generally a lower temperature requiring a somewhat longer immersion time to'effect comparable results.

While the specific proportions and exact times and temperatures noted above are given by way of example, it is to be understood that this is illustrative of a preferred method of carrying out the invention rather than a necessary limitation thereof, and it is my intention to claim the invention broadly as hereafter defined and restricted only by the prior art.

This is a continuation-in-part of my pending application on Cleaning Solution and Method, filed November 8, 1943, Serial No. 509,474, now abandoned.

I claim:

l. A liquid, metal cleaning composition consisting essentially of 1 Per cent by weight Ethylene diamine About 12 Water About 4 Neutral coal tar oil About 68 Oleic acid About 6 Pine oil About 10 2. A process for removing deposits produced on a metal surface by heated oil, said process comprising subjecting said surface to the action of a liquid, metal cleaning composition consisting essentially of:

Per cent by weight Ethylene diamine About 12 Water About 4 Neutral coal tar oil About 68 Oleic acid About 6 Pine oil About 10 and then flushing said metal surface with water.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ind. & Eng. Chem, Aug. 1935, pages 867-871. Chemical 'Formulary, Bennett, vol. 6 (1943), pages 494-495. 

1. A LIQUID, METAL CLEANING COMPOSITION CONSISTING ESSENTIALLY OF: 